Texturing multiple books
Here, you can try something like this:

The main ingredient in getting different color books is the RANDOM output of an OBJECT INFO node. For this to work, the books must all be separate objects, so do what you already did - array the books, apply the array and separate by loose parts. Once this is done, you can apply the same material to all books (I used 2 - one for the cover and another for the pages), and the random output will generate a random color for each book. I didn't like the default colors it gave me so I mixed it with a bunch of others. That's what most of the nodes in the color section are. Play with them yourself to get different looks.

Another option is to run the black and white output of the random through a ColorRamp node. You can use a mix shader to change the degree of variation, and a &quot;constant&quot; ColorRamp setting to choose your own color scheme. However, I liked the selection given by the color mix to be more varied, especially when mixed with additional colors. (You can see at the end of the chain, one of the last steps to is to multiply by red. If you turn the mix factor up to 1, the red dominates all of the books and reminds me of the &quot;books of knowledge&quot; Britannica series of encyclopedias - my personal favorite) Use your own preference, however.

For the bands around the books, I used 2 different Wave Textures and lightened the mix to get 2 nice bands at the top and bottom.  (You can achieve this with only one wave texture if needed, I just used 2 because I was playing with different combinations). I sharpened their cut-offs with 2 ColorRamps - one for the color (yellowish for gold), and the other to be used as the basis for a mask, as well as the roughness factors, and (inverted) for the metallic (bands).

I used a noise texture, scaled up, to make the &quot;bumps&quot; on the covers. The mix node where I combine the noise with a light grey color has the effect of dampening the values of the noise so it loos more realistic. I mixed this combination with the (B&amp;W) bands I already made to create a height-map of sorts, showing the bumps and making the bands appear to &quot;stick out&quot; from the books.

Finally, I used some ambient occlusion information combined with another noise texture to add &quot;depth and wear&quot; to the books. I turned on screen space reflections and ambient occlusion in the render properties panel, and lastly, added an HDRI for some better &quot;reflections&quot;. The final result looks like this:

If you have UV unwrapped your books, you can also use a base &quot;cover image&quot; texture and randomize the colors by mixing them the same way as well, if you want. I'll post the .blend file, so anyone who wants can play around.
File is here - 
Hope this helps